Advertising experts know more about how you think than you do. If given a choice between a Large popcorn at $7 and a Small popcorn at $3, most people choose the Small because the Large looks too expensive. When a third choice is added, a Medium popcorn at $6, most people choose the Large popcorn because it is now only $1 more than the Medium, therefor it looks like a better value. Your brain just tricked you because the human brain makes some of its decisions by comparison. Many other such brain-tricking tools are known and used by advertisers, politicians, magicians, proselytizers, issue champions and others. $14.99 instead of $15.00 is proven to actually work as long as you don't know you are being manipulated.
"In almost every act of our daily lives, whether in the sphere of politics or business, in our social conduct or our ethical thinking, we are dominated by the relatively small number of persons...who understand the mental processes and social patterns of the masses. It is they who pull the wires which control the public mind.” ― Edward L. Bernays